1. Field of the Invention
The invention relates to a device and a method for the dosed delivery of fluid.
2. Description of the Prior Art
The significance of the demand for a precise dosing of a fluid is increasing, for instance in gasoline direct injection in the context of designing a lean-mix engine. With a lean-mix engine design, a reduction of the CO.sub.2 exhaust is intended.
For purposes of realizing a lean-mix engine, a high requirement is established for dosing of the fuel, namely a simultaneous axially symmetric fuel distribution, use of the engine given high temperature gradients of approximately 150.degree., a high injection pressure up to 250 bars, a short drive-dead-time of less than 0.1 ms, and a short switching time of less than 0.15 ms, among other things.
This requirement can be only insufficiently met using an electromagnetically driven dosing mechanism due to the limited switching time. A piezoelectric actuator, on the other hand, is characterized by a very short response time and dead time. However, given the use of a piezoelectric direct drive, the insufficient compensation of length modifications of the piezoactuator and housing which are conditioned by temperature effects or by aging and settling effects is disadvantageous. Also, a piezoactuator of great structural length is required for this, which is disadvantageous to production and is expensive.
In addition, a piezoelectric actuator combined with a membrane hydraulic results in problems such as, a mechanical calibration involving great outlay, a danger of breaking the membrane, and a low degree of effectiveness.
German Offenlegungsschrift 43 06 073 teaches a measuring device for fluids wherein a piezoelectric actuator via a fluid-filled chamber, drives a lifting element that controls a fluid delivery. This device has the disadvantage of a high outlay and a vulnerable design in the drive field, as well as a separation of the hydraulic circuits at the drive side and at the injection side.
German Offenlegungsschrift 195 19 191 discloses an injection valve wherein the movement of a piezoactuator directly controls a tappet by means of a piston-hydraulic stroke translation. This valve is reliant on the use of control surfaces at the valve tappet. Furthermore, a motion-commutating stroke translation is disclosed which presupposes a development for the hydraulic chamber that is expensive. The fluid is also delivered via at least one injection opening, whereby the danger of an occlusion exists, and whereby an axially symmetric fuel delivery is also strongly prevented.